My U.S. Pat. No. 3,789,505 of Dec. 5, 1974 discloses a multi-core magnetic head of non-magnetic and magnetic ceramic material, especially ferrite material. The magnetic ferrite material is glass bonded to the non-magnetic ferrite material. The disclosure of my earlier patent is hereby incorporated by reference.
U.S. Pat. No. 3,024,318 to Duinker et al discloses the use of a glass gap spacer for magnetic heads.
The prior art has been unable to utilize the properties of manganese-zinc ferrite material as the magnetic ceramic of such magnetic heads, as the manganese-zinc ferrite has an affinity for oxygen and reacts with air as well as with the glass bonding composition. The reaction between the glass and the ferrite produces stresses in the ferrite, which have resulted in mechanical defects in the ferrite.
The technique of glass bonding ferrite materials for recording head applications has long been an accepted method in the prior art for producing gaps in magnetic materials, with the gaps generally ranging from 10-250 microinches in width; and occasionally as great as 500 microinches in width. However, the heads produced by the conventional glass bonding technique have used nickel-zinc ferrite materials and not manganese-zinc ferrite materials, because of the above manganese-zinc ferrite reaction problem. The glass actually appears to etch away the surface of manganese-zinc ferrite, and the glass may migrate into the boundaries of the ferrite.
Various techniques can occasionally result in glass bonded manganese-zinc ferrites with reduced reaction between the glass and the manganese-zinc ferrite. Such techniques include, for instance, the use of a vacuum in the glass bonding step. However, the prior art has never been able to eliminate the reaction between the glass and the manganese-zinc ferrite.
The Treptow U.S. Pat. No. 3,029,559 discloses a method of bonding glass to metal surfaces using an interface layer of various finely-divided metals, including nickel, iron, cobalt, platinum, molybdenum, tungsten, copper, silver and gold. These metals are applied to the substrate surface in the form of powders, and sintered in a non-oxidizing or reducing atmosphere. The amount of intermediate layer applied is insufficient to form an integral film, and the patentee desires to form a joint bonding of the glass to both the substrate and the metal sintered thereon (note column 3, first full paragraph).
The Rohrer U.S. Pat. No. 3,404,968 is directed to solving problems of metal embrittlement and disintegration by oxidation associated with the manufacture of glass-to-metal seals. The patentee forms a first intermediate layer of nickel and chromium above a metal substrate, and then forms a second layer of chromium oxide, preferably by oxidizing chromium in the first layer. The glass is then bonded to the chromium oxide layer.
My co-pending patent application Ser. No. 697,842, filed June 21, 1976, now U.S. Pat. No. 4,048,714, discloses a method of minimizing reactions between a surface of manganese zinc ferrite and a glass bonding compositions applied thereto, while minimizing oxidation of the manganese in the ferrite, by forming an intermediate barrier layer on the manganese zinc ferrite surface prior to the application of the glass bonding composition. The glass bonding composition is preferably a high lead glass bonding composition, which can be fired at a temperature below 700.degree. C., preferably below 500.degree. C.
The assembly of my aforesaid U.S. patent application Ser. No. 697,842 produces magnetic recording/reproducing heads which have improved wear resistance, as compared to heads having substantial gaps of glass bonding composition, such as U.S. Pat. No. 3,795,954, Alex et al.